1. Field of the Invention
This invention relates to a solar cell module, particularly relates to a two-side incidence type solar cell module capable of entering light from both front and rear surfaces provided with transparent front and rear surface members.
2. Description of Prior Art
Because solar light is unexhausted energy, a solar cell device for directly converting light energy into electrical energy has been developed as energy source for substituting with environmentally harmful fossil fuel such as petroleum and coal. A plurality of solar cell elements are electrically connected in series or in parallel with each other to form a solar cell module and increase an output. And the solar cell module can be used as a practical energy source.
A conventional solar cell module which generates power on a one side surface is so structured that a plurality of solar cell elements 110 between a front surface glass 100 and a rear surface member 101 are sealed with transparent and insulative resin 102 such as EVA (ethylene vinyl acetate).
The solar cell element 110 contains semiconductor material such as single crystalline silicon, polycrystalline silicon, or the like, and the solar cell elements 110 are connected in series by connection member 111 of a metal thin plate such as a copper foil plate or the like. The rear surface member 101 has a lamination film with a metal foil such as an aluminum (Al) foil or the like sandwiched with plastic films so that water entrance from a rear surface can be prevented.
The solar cell module is integrally formed by sandwiching the solar cell element 110 between the front surface glass 100 and the rear surface member 101 with a resin sheet of EVA or the like of 0.4-0.8 mm in thickness interposed and heating it at a reduced pressure.
On the other hand, a two-side incidence type solar cell element has been proposed, which is so structured that an electrode on a rear surface not only an electrode on a front light incidence side is a transparent electrode. With this structure, light is incident from both of the front and rear surfaces of the solar cell element. The rear surface of this solar cell element is formed of transparent material.
In the meantime, a solar cell module should be weather proof in order to withstand long-term use in outside. The above conventional two-side incidence type structure uses transparent material for the rear surface member. When a transparent resin film is used as the rear surface member, water is likely to enter as compared with a lamination film with a metal foil sandwiched with plastic films. Therefore, it is necessary to take water penetration into consideration. Although a film of a small water vapor transmission rate has been proposed as a transparent resin film, it still requires to be improved.
This invention was made to solve this problem and provides a solar cell module capable of improving reliability by improving moisture proofness.
Furthermore, this invention was made to improve reliability of the solar cell module by reducing water reaching to the front surface glass when the rear surface member is the resin film and suppressing the sodium ions deposited from the front surface glass from reaching to the front surface of the solar cell elements.
A solar cell module of this invention comprises a light transmitting member on a front surface side containing at least sodium, a rear surface member, a plurality of solar cell elements sealed with sealing resin between the light transmitting member on the front surface side and the rear surface member, and a sodium diffusion preventive function layer for preventing diffusion of sodium from the light transmitting member on the front surface side arranged between the light transmitting member on the front surface side and the solar cell elements.
The light transmitting member on the front surface side is glass, and the rear surface member is a transparent resin film.
The sodium diffusion preventing layer in this structure can suppress the sodium ions from reaching to the solar cell element and the moisture proofness can be improved. Degradation of power generation performance of the solar cell retards and a solar cell module of high reliability capable of withstanding long-term use in outside can be provided.
The sodium diffusion preventive function layer is sealing resin of not less than 1.0 mm in thickness arranged between the light transmitting member on the front surface side and the solar cell element.
With this structure, a distance between the front surface glass and the solar cell element can increase and the sodium ions deposited from the front surface glass retard from reaching to the solar cell element. Therefore, degradation of power generation performance of the solar cell retards and a solar cell module of high reliability capable of withstanding long-term use in outside can be provided.
The sodium diffusion preventive function layer is a resin layer of smaller water vapor transmission rate than that of the sealing resin.
With this structure, the sodium ions deposited from the front surface glass can be blocked at the resin layer of smaller water vapor transmission rate, and degradation of power generation of the solar cell element can be prevented.
The resin layer is a resin film inserted between the light transmitting member on the front surface side and the solar cell element.
The resin film is inserted at least in a region corresponding to the solar cell element.
The resin film is a PET film.
With this structure, the sodium ions deposited from the front surface glass can be blocked by the PET film, and degradation of power generation performance at the solar cell element can be prevented.
The sodium diffusion preventive function layer can be formed on a surface on a side of the sealing resin of the light transmitting member on the front surface side, and can be formed of an inorganic oxide layer, a nitride layer, or a fluoride layer.
With this structure, the sodium ions are prevented from reaching to the solar cell element, and the moisture proofness can be improved.
The sodium diffusion preventive function layer is formed by reforming process of a surface of the light transmitting member on the front surface side.
When reforming a surface of the glass, the sodium in the glass easy to move is molten out in the molten salt, and alkaline in the molten salt is diffused in the glass. As a result, deposition of the sodium ions from the glass is reduced to suppress the sodium ions from reaching to the solar cell element and improve the moisture proofness.
The sodium diffusion preventive function layer can be formed of glass member containing not more than 5 wt. % of sodium.
Thus, deposition of the sodium ions is prevented because the sodium contained is less, and the sodium ions are suppressed from reaching to the solar cell element to improve the moisture proofness.
The water vapor transmission rate of the transparent resin film is not more than 6.3 g/m2xc2x7day.
With this structure, increase of water in the sealing resin between the front surface glass and the solar cell element can be prevented.
An inorganic oxide layer, a nitride layer, or a fluoride layer may be formed on a surface of the transparent resin film.
The inorganic oxide layer, the nitride layer, or the fluoride layer has water barrier properties and function as a water vapor transmission preventing layer.